Method of lower profile mems package with stress isolations

ABSTRACT

MEMS packages, modules, and methods of fabrication are described. In an embodiment, a MEMS package includes a MEMS die and an IC die mounted on a front side of a surface mount substrate, and a molding compound encapsulating the IC die and the MEMS die on the front side of the surface mount substrate. In an embodiment, a landing pad arrangement on a back side of the surface mount substrate forms and anchor plane area for bonding the surface mount substrate to a module substrate that is not directly beneath the MEMS die.

RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 14/568,845 filed Dec. 12, 2014, which is incorporated herein byreference.

BACKGROUND

Field

Embodiments described herein relate to semiconductor packaging. Moreparticularly embodiments relate to MEMS packages, modules, and methodsof fabrication.

Background Information

As electronic products are becoming increasingly sophisticated and thesize of the overall packages is reduced to meet market needs, theseadvances are associated with various packaging challenges to reduce costand form factor of the packages. In addition as the market drivesthinner package profiles, it becomes more difficult to manage straininduced performance drift.

Micro-electro-mechanical systems (MEMS) die can be formed fromcustomized integrated circuits, and have become a significant growtharea in consumer space. MEMS are often used to sense environmentalcharacteristics or act as a user input for electronic products. However,MEMS devices such as gyroscopes, accelerometers, microphones, pressuresensors, environmental sensors and magnetometers are all sensitive tostrain induced performance drift and can have unique packaging andmounting requirements compared to some general purpose integratedcircuit (IC) die.

SUMMARY

MEMS packages, modules, and methods of formation are described. In anembodiment, a MEMS package includes an IC die mounted on a front side ofa surface mount substrate, and a MEMS die mounted on the front side ofthe surface mount substrate laterally adjacent to the IC die. The MEMSdie and IC die can be mounted on the surface mount substrate using avariety of methods, including a die attach film with wire bonding orflip chip bonding. A molding compound encapsulates the IC die and theMEMS die on the front side of the surface mount substrate. The moldingcompound may be formed directly on the surface mount substrate. Themolding compound may be formed directly over the MEMS die, oralternatively may not cover a top surface of the MEMS die, for example,so that the MEMS die is exposed to ambient environment. In anembodiment, a landing pad arrangement, including all landing pads on aback side of the surface mount substrate, surrounds a periphery of theIC die on the front side of the surface mount substrate and does notsurround a periphery of the MEMS die on the front side of the surfacemount substrate. A plurality of conductive bumps (e.g. solder balls) maybe placed on the landing pads, with each landing pad havingcorresponding conductive bump.

In an embodiment, a trench is in a top surface of the molding compoundbetween the IC die and the MEMS die. In an embodiment, one or moreopenings are formed in the surface mount substrate between the IC dieand the MEMS die. The size and shape of the trench and opening(s) may beused for isolating the MEMS die from package and module stress. In anembodiment, a bottom surface of the trench is below a top surface of theMEMS die.

In an embodiment, a module includes a module substrate, and the MEMSpackage bonded to the module substrate. In an embodiment, thearrangement of conductive bumps corresponds to an anchored area of thesurface mount substrate directly over the module substrate. A hangingarea of the surface mount substrate laterally extends from the anchoredarea of the surface mount substrate, and a conductive bump is not formeddirectly beneath the hanging area of the surface mount substrate. Insuch a configuration an air gap may exist directly between a back sideof the surface mount substrate and the module substrate. Variousconfigurations are described that may protect the hanging portion fromflexing to the point that the conductive bumps fracture. For example,one or more bumpers may optionally be formed on the module substratedirectly beneath the hanging area of the surface mount substrate. An airgap may exist directly between the back side of the surface mountsubstrate and the bumper(s). One or more bumpers may optionally beformed on a back side of the surface mount substrate directly beneaththe hanging area of the surface mount substrate. An air gap may existdirectly between the bumper(s) and the front side of the modulesubstrate. Other structural features may be used to provide mechanicalprotection. For example, a metal trace, and or solder mask can be formedon either or both of the back side of the surface mount substrate andthe front side of the module substrate directly beneath the hangingarea. In an embodiment, the solder mask covers the metal trace. In thismanner, height of the metal traces and/or solder mask layers can formprotruding structures for protecting against excessive bending of thehanging area.

In an embodiment, a plurality of other components are bonded to the topside of the module substrate, and encapsulated in a second moldingcompound on the top side of the module substrate. For example, theplurality of other components and the second molding compound maycorrespond to a mold array package (MAP) configuration. In anembodiment, a top surface of the molding compound encapsulating the ICdie and the MEMS die is below a top surface of the second moldingcompound encapsulating the plurality of other components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view illustration of a module includinga MEMS package with a stacked die configuration.

FIG. 2 is a cross-sectional side view illustration of a module includinga MEMS package a side-by-side die configuration in accordance with anembodiment.

FIG. 3 is schematic back side view illustration of a MEMS package inaccordance with an embodiment.

FIG. 4A is a cross-sectional side view illustration of a MEMS package inaccordance with an embodiment.

FIG. 4B is a cross-sectional side view illustration of a MEMS package inaccordance with an embodiment.

FIG. 5 is a close up cross-sectional side view illustration of a MEMSpackage bonded to a module substrate in accordance with an embodiment.

FIG. 6 is a cross-sectional side view illustration of a strained MEMSmodule in accordance with an embodiment.

DETAILED DESCRIPTION

Embodiments describe MEMS packages, modules, and methods of fabrication.In various embodiments, description is made with reference to figures.However, certain embodiments may be practiced without one or more ofthese specific details, or in combination with other known methods andconfigurations. In the following description, numerous specific detailsare set forth, such as specific configurations, dimensions andprocesses, etc., in order to provide a thorough understanding of theembodiments. In other instances, well-known processes and manufacturingtechniques have not been described in particular detail in order to notunnecessarily obscure the embodiments. Reference throughout thisspecification to “one embodiment” means that a particular feature,structure, configuration, or characteristic described in connection withthe embodiment is included in at least one embodiment. Thus, theappearances of the phrase “in one embodiment” in various placesthroughout this specification are not necessarily referring to the sameembodiment. Furthermore, the particular features, structures,configurations, or characteristics may be combined in any suitablemanner in one or more embodiments.

The terms “above”, “over”, “to”, “between” and “on” as used herein mayrefer to a relative position of one layer with respect to other layers.One layer “above”, “over” or “on” another layer or bonded “to” or in“contact” with another layer may be directly in contact with the otherlayer or may have one or more intervening layers. One layer “between”layers may be directly in contact with the layers or may have one ormore intervening layers.

In one aspect, embodiments describe MEMS packages, modules, and mannersof fabrication which may address MEMS package and module stress. It hasbeen observed that MEMS devices are sensitive to stress. For example,stress transfer to a MEMS die from an underlying substrate (such assurface mount substrate and module substrate) can cause MEMSdevice/sensor output shift. In addition, stress impact to device/sensoroutput change may become more serious when MEMS package thickness andform factor are further reduced to meet market needs.

In another aspect, embodiments describe MEMS packages, modules, andmanners of fabrication which may enable reduced MEMS package profile andoverall module profile. In an embodiment, a MEMS die and integratedcircuit (IC) die are mounted side-by-side on a surface mount substrate.In such an arrangement, MEMS die thickness may be maintained withoutsacrificing the strain sensitivity of the MEMS die. It has been observedthat thicker MEMS die may be less sensitive to strain then thinner MEMSdie. Thus, as consumer devices, particularly mobile and wearabledevices, continue to become thinner with increased functionality,further reduction in MEMS die thickness may be met with a tradeoff ofincreased strain induced performance drift. A side-by-side configurationmay also allow for a reduced MEMS package height and resulting moduleheight, particularly where a MEMS die component thickness is asignificant barrier to z-height profile reduction of the MEMS packageand module. Thus, while a side-by-side configuration may possiblyincrease the footprint of a MEMS package, in accordance with someembodiments, MEMS die thickness can be maintained at a sufficientthickness for reduced susceptibility to strain.

In another aspect, embodiments describe a MEMS packages and modules withlow profiles, low strain susceptibility, and low temperature coefficientof offset (TCO) for a contained MEMS device. The offset error of adevice/sensor due to temperature is due to TCO. This parameter is therate of change of the offset when the device/sensor is subject totemperature. Where TCO is high, the device/sensor may require offsetcalibration. Lower TCO may allow for higher resolution devices/sensorsand less offset calibration. In accordance with embodiments, MEMSpackages and modules are described that may include low profiles, andspecific structures for stress management or isolation resulting inimproved TCO and MEMS device or sensor operation.

In an embodiment, an air gap technique is described in order toalleviate the impact of stress transfer from underlying substrates toMEMS devices. In an embodiment, a MEMS die and IC die are mountedside-by-side on a surface mount substrate, which in turn is bonded to amodule substrate such as a printed circuit board (PCB). In anembodiment, the surface mount substrate is anchored to the modulesubstrate with an arrangement of conductive bumps such that a portion ofthe package substrate includes an anchored area directly over the PCB,and a hanging area. In an embodiment, the MEMS die is mounted on thesurface mount substrate in the hanging area of the surface mountsubstrate. For example, the surface mount substrate may be bonded to amodule substrate in a cantilever-type configuration. Additional featuresmay be included for additional stress isolation, and reduced strainsusceptibility of the MEMS die. In an embodiment a partial cut or trenchis created in a top surface of a molding compound that encapsulates theside-by-side MEMS die and IC die, with the partial cut or trench locatedbetween the MEMS die and the IC die. In an embodiment, one or more slotsor holes are formed in the surface mount substrate between theside-by-side MEMS die and IC die.

As used herein, “encapsulating” does not require all surfaces to beencased within a molding compound. For example, referring briefly toFIG. 5 the lateral sides of MEMS die 302 are encased in molding compound310, while the molding compound is not formed over the top surface ofthe MEMS die 302. As will become apparent in the following description,the height of the molding compound 310 may contribute to the overallz-height of the MEMS package and module. Accordingly, in someembodiments, the amount of molding compound is controlled to achieve aspecified height. In accordance with embodiments, MEMS devices such aspressure sensors, microphones, and environmental sensors for sensingtemperature, humidity, and gas can have unique packaging and mountingrequirements since the MEMS devices often require exposure to an ambientexternal environment, such as an ambient environment of a user using theelectronic product having the MEMS device. In some embodiments, anamount of the molding compound 310 is controlled in order to expose thetop surface of the MEMS die 302 so that it is exposed to ambientenvironment. However, it is not required that that the top surface ofthe MEMS die 302 is exposed in all embodiments, and the molding compound310 may cover the top surface of the die 302. For example, it may not berequired for MEMS devices such as accelerometers, magnetometers, andgyroscopes to be exposed to the ambient environment.

A variety of surface mount substrates can be used in accordance withembodiments, such as land grid array (LGA), ball grid array (BGA), quadflat no-leads QFN, or ceramic substrates. In an embodiment, flip chipbonding is used as the surface mount interconnection method forelectrically connecting the surface mount substrate to the modulesubstrate.

Referring now to FIG. 1, a cross-sectional side view illustration isprovided of a module including a MEMS package 300 with a stacked dieconfiguration. As illustrated the module includes a MEMS package 300bonded to a module substrate 100 with conductive bumps 316. A pluralityof additional components, illustrated as 202, 204, and 206 are alsobonded to the module substrate and encapsulated within a moldingcompound 210 on the module substrate. For example, the module substrate100 may be a printed circuit board (PCB), ceramic panel, leadframe, orwafer. The components 202, 204, 206 can be any combination of numerouspassive or active components. The assembled components 202, 204, 206 maybe arranged on the module substrate 100 in a mold array package (MAP)configuration in which each of the components 202, 204, 206 isencapsulated within a single molding compound 210 on a top side 101 ofthe module substrate 100. Together, the components 202, 204, 206 andmolding compound 210 may be considered as a MAP 200. The moldingcompound 210 may cover a top surface of each of the components 202, 204,206.

As illustrated in FIG. 1, a MEMS package 300 is bonded to a top side 101of the module substrate 100 outside the area reserved for the MAP 200.For example, this may aid in stress isolation and operation of the MEMSdie 302. The particular MEMS package 300 illustrated in FIG. 1 includesa stacked-die arrangement in which a MEMS die 302 is stacked onto an ICdie 304. As shown, the MEMS die 302 includes a base substrate 302A and acap 302B. The particular arrangement is meant to be exemplary, andnon-limiting. The exemplary MEMS package 300 includes a surface mountsubstrate 312, an IC die 304, such as an application specific integratedcircuit (ASIC) die, attached to the surface mount substrate 312 with adie attach film 308, and a MEMS die 302 attached to the IC die 304 witha die attach film 306. Wire bonds 314 are used to provide electricalconnection between the MEMS die 302, IC die 304, and surface mountsubstrate 312. A molding compound 310 of a molding compound encapsulatesthe die and wire bonds on the surface mount substrate 312.

In the particular configuration illustrated in FIG. 1, the profileheight of the MEMS package 300 is illustrated as being greater than aprofile height of the MAP 200 on the same side of the module substrate100. The height difference (+h) between the top surface 311 of the MEMSpackage 300 and the top surface 211 of the MAP 200 may be attributed tothe thickness of the MEMS die 302 or die stacking within the MEMSpackage 300. It has been observed that thicker MEMS die 302 may be lesssensitive to strain than thinner MEMS die. Thus, as consumer devices,particularly mobile and wearable devices, continue to become thinnerwith increased functionality, further reduction in MEMS die 302 and MEMSpackage 300 thickness may be met with a tradeoff of increased straininduced performance drift.

Referring now to FIG. 2, in accordance with embodiments a MEMS package400 is illustrated including a MEMS die 302 and IC die 304 mounted on afront side of a surface mount substrate 312 in a side-by-sideconfiguration. In the embodiment illustrated in FIG. 2, MEMS die 302thickness may be maintained at a sufficient thickness for reducedsusceptibility to strain. In the embodiment illustrated, surface mountsubstrate 312 is bonded to the module substrate 100 with an arrangementof conductive bumps 316 including all of the conductive bumps bondingthe surface mount substrate 312 to the module substrate 100. Thearrangement of conductive bumps 316 corresponds to an anchored area 330of the surface mount substrate directly over the module substrate. Thesurface mount substrate 312 additionally includes a hanging area 332that laterally extends from the anchored area 330 in which a conductivebump 316 is not formed directly underneath the hanging area 332 of thesurface mount substrate 312. Still referring to FIG. 2, the IC die 304(e.g. ASIC die) is mounted on the front side 313 of the surface mountsubstrate 312 in the anchored area 330 of the surface mount substrate,and the MEMS die 302 is mounted on the front side 313 of the surfacemount substrate 312 in the hanging area 332 of the surface mountsubstrate 312. In the exemplary MEMS package 400, the IC die 304 ismounted on the surface mount substrate with a die attach film 308, andthe MEMS die 302 is mounted on the surface mount substrate with a dieattach film 306. Wire bonds 314 are used to provide electricalconnection between the MEMS die 302, IC die 304, and surface mountsubstrate 312 in the illustrated embodiment. Wire bonds 314 can also beused for die-to-die interconnection between MEMS die 302 and IC die 304.In another embodiment, the IC die 304 and/or the MEMS die 302 may bemounted on the surface mount substrate, for example as a flip chipattachment with no wire bonds. Such a configuration is illustrated inFIG. 4B. A variety of alternative attachment method may be used formounting the MEMS die and IC die on the surface mount substrate. Inaccordance with embodiments, molding compound 310 (e.g. epoxy)encapsulates the IC die 304 and the MEMS die 302 on the front side 313of the surface mount substrate 312. The molding compound 310 may beformed directly on the front side 313 of the surface mount substrate. Inthe particular embodiment illustrated, the molding compound 310 does notcover the top surface of the MEMS die 302, and is illustrated as beingflush with the top surface of the MEMS die 302. For example, this mayallow the MEMS die 302 to be exposed to the ambient atmosphere. Themolding compound 310 may alternatively cover the top surface of the MEMSdie 302.

As shown in FIG. 2, the profile height of the MEMS package 400 isillustrated as being less than a profile height of the MAP 200 on thesame side of the module substrate 100. The height difference (−h)between the top surface 311 of the MEMS package 400 and the top surface211 of the MAP 200 may be attributed to the side-by-side arrangement ofMEMS die 302 and IC die 304. The side-by-side arrangement, mayadditionally allow for a thicker MEMS die 302, which may be lesssensitive to strain than thinner MEMS die. For example, the MEMS die 302illustrated in FIG. 2 could be made thicker for improved performance,with a total thickness increase equivalent to (-h) without affecting theoverall module thickness. In an embodiment, the profile height of theMEMS package 400 on the module substrate 100 is approximately the sameas the profile height of the MAP 200 on the same side of the modulesubstrate 100.

In an embodiment, the surface mount substrate 312 is bonded to themodule substrate 100 in a cantilever-type configuration, in which theanchored area 330 corresponds to a fixed end of the cantilever and thehanging area 332 corresponds includes a free end opposite the fixed end.In an embodiment, an air gap 324 exists between the back side 317 of thesurface mount substrate 312 and the module substrate 100. In anembodiment, one or more bumpers 320 are formed on the module substrate100 directly beneath the hanging area 332 of the surface mount substrateto protect the bonded area between the surface mount substrate andmodule substrate (corresponding to the conductive bumps 316) frombreaking. Alternatively, or in addition to, one or more bumpers 320 maybe formed on the back side 317 of the surface mount substrate 312 in thehanging area 332 to protect the bonded area between the surface mountsubstrate and module substrate from breaking. For example, the one ormore bumpers 320 may aid in drop and shock resistance of the bonded MEMSpackage 400. In an embodiment, the one or more bumpers 320 are formed ofan elastomeric material. In an embodiment, the air gap 324 is alsodirectly between the one or more bumpers 320 and either the surfacemount substrate or module substrate, depending on location of the one ormore bumpers. Additional structures for providing mechanical protectionto the bonded area are described below with regard to FIG. 5 inaccordance with embodiments.

Still referring to FIG. 2, in an embodiment a trench 322 is located inthe top surface 311 of the molding compound 310 (which also correspondsto the top surface of the MEMS package 400 in FIG. 2) between the IC die304 and the MEMS die 302. The trench 322 may be formed during themolding process. Trench 322 may also be formed after the moldingprocess, for example by using a mechanical blade or laser. In anembodiment, the depth, length, and width of the trench is designed toachieve mechanical integrity for handling and stress isolation. Forexample, the trench may isolate the MEMS die 302 from induced stresstransfer from the underlying substrates (surface mount substrate and/ormodule substrate) including mechanical stress, thermal mechanicalstress, and hygroscopic stress. For example, the trench may isolatestress transfer from mechanical stress in the surface mount substrateand/or module substrate (e.g. from screws in the module substrate),thermal mechanical stress (e.g. associated with a higher coefficient ofthermal expansion (CTE) of the module substrate), or hygroscopic stress(e.g. associated with moisture absorption by the module substrate). Inan embodiment, a bottom surface 323 of the trench 322 is below a topsurface 303 of the MEMS die 302.

In an embodiment, one or more openings 340 are optionally formed in thesurface mount substrate 312 between the IC die 304 and the MEMS die 302.In an embodiment, the one or more openings 340 extend entirely throughthe surface mount substrate 312. Openings 340 may be in the form ofslots or holes, for example. In an embodiment, the size of the openings340 isolate the MEMS die 302 from induced stress transfer from thesurface mount substrate and/or module substrate including mechanicalstress, thermal mechanical stress, and hygroscopic stress.

Referring now to FIG. 3 a schematic back side view illustration isprovided of a MEMS package 400 in accordance with an embodiment. In theparticular illustration provided in FIG. 3, only certain features areincluded in order to illustrate the relationship of specific features.FIGS. 4A-4B are cross-sectional side view illustrations of MEMS packages400 in accordance with embodiments. For example, in FIG. 4A the IC die304 and MEMS die 302 are illustrated as being bonded to the surfacemount substrate 312 with die attach films 308. In FIG. 4B the IC die 304and MEMS die 302 are illustrated as being flip chip bonded to thesurface mount substrate 312 with conductive bumps 316. In accordancewith embodiments, a number of combinations of bonding methods may beused for bonding the IC die and MEMS die to the surface mount substrate,and it is not required for the same bonding method to be used for boththe IC die and MEMS die. In the following description, features in anyor all FIGS. 3-4B are discussed concurrently. As shown in FIGS. 3-4B, anarrangement of landing pads 318 is on a back side 317 of the surfacemount substrate 312. Conductive bumps 316 (e.g. solder balls) mayoptionally be placed on landing pads 318 for bonding to a modulesubstrate. In an embodiment, the landing pad 318 arrangement surrounds aperiphery of the IC die 304 on the front side 313 of the surface mountsurface and does not surround a periphery of the MEMS die 302 on thefront side of the surface mount substrate. In an embodiment, the landingpad 318 arrangement does not overlap the periphery of the MEMS die 302.The peripheries of the IC die 304 and MEMS die 302 are illustrated asdotted lines in FIG. 3. As illustrated, the landing pads 318 are offsetsuch that they are located only underneath a proximity of the IC diearea, rather than underneath the MEMS die area.

As described above, the dimensions of the trench 322 and/or opening 340may be designed to achieve mechanical integrity for handling andisolation of the MEMS die 302 from induced stress transfer. In anembodiment, at least one x-y dimension of the trench 322 is smaller thanan x-y dimension of the molding compound 310. In the embodimentillustrated in FIG. 3 the trench 322 is formed entirely across the widthof the molding compound 310 between the IC die 304 and MEMS die 302.Location and dimensions of the trench 322 may be adjusted so that wires314 are not exposed, if present. In the embodiment illustrated, a widthof the slot shaped opening 340 is greater than a width of the MEMS die302 in the same direction. Width and length, and potentially depth, ofthe one or more openings 340 may be adjusted to accommodate routingwithin the surface mount substrate 312. In an embodiment, a plurality ofopenings 340 are formed through the surface mount substrate between theIC die 304 and MEMS die 302. In an embodiment, the openings 340 arelocated in an area of the outside of the landing pad 318 arrangement inthe hanging area 332 of the surface mount substrate.

FIG. 5 is a close up cross-sectional side view illustration of a MEMSpackage bonded to a module substrate in accordance with an embodiment.As described above, it is not required for the molding compound 310 tocover the top surface of the MEMS die 302. For example, as shown in FIG.5 a vent hole 305 in the top surface of the cap 302B is exposed to allowexposure of the MEMS device within the IC die to ambient atmosphere.

As described above, various structures may be included to providemechanical protection to the bonded area corresponding to conductivebumps 316 that bonded to the landing pads 118, 318 on the modulesubstrate 100 and surface mount substrate 312. In an embodiment, one ormore bumpers 320 are formed on the back side 317 of the surface mountsubstrate 312 and/or top side 101 of the module substrate 100. In anembodiment, a metal trace 118, 318 (e.g., Cu) and/or solder mask 152,352 can be formed on either or both of the back side of the surfacemount substrate and the front side of the module substrate directlybeneath the hanging area. Solder masks 152, 352 may be formed of anysuitable material such as, but not limited to, epoxy or polyimide. In anembodiment, an exemplary standoff height for conductive bumps 316 may beapproximately 20-50 μm. In an embodiment, metal traces 118, 318 may beapproximately 5-15 μm thick. Thus, by tailoring the thickness of theconductive bumps 316, metals traces, and/or solder masks 152, 352 andappropriate air gap 324 thickness can be provided directly underneaththe hanging area 332 for protecting against excessive bending of thehanging area. Height of optional bumpers 320 can similarly bedetermined. In an embodiment, a bumper 320 is formed directly over asolder mask 152, 352, and may be formed directly on a solder mask.

Referring now to FIG. 6, a cross-sectional side view illustration isprovided of a strained MEMS module in accordance with an embodiment. Forexample, the module substrate 100 may be warped due to thermal expansionor hygroscopic stress. In the particular embodiment illustrated, themodule substrate 100 has a “cry” shape. In such a configuration, thebottom surface of the module substrate may be under compressive strainwith the top surface onto which the MEMS package 400 is bonded undertensile strain. The particular strain relationship illustrated in FIG. 6is exaggerated to illustrate immunity to bending strain that may beachieved in accordance with embodiments. As shown, as the modulesubstrate 100 is bent, stress is transferred directly into the anchoredarea 330. The transferred stress may also result in strain in theanchored area 330 of the surface mount substrate 312, and potentiallybending of the surface mount substrate in the anchored area 330. Thisstress is transferred to components mounted in this region of thesurface mount substrate. In accordance with embodiments, since thehanging area 332 is not directly attached to the module substrate 100less strain is transferred to the hanging area 332, and consequently toany components mounted in the hanging area. Thus, the hanging area mayexhibit less bending, and stress transfer to the MEMS die 302.

In the embodiment illustrated in FIG. 6, the back side 317 of thesurface mount substrate 312 in the anchored area 330 may be undercompressive stress caused by the module substrate 100. Similarly, thetop surface 311 of the molding compound may be under tensile stress. Inaccordance with embodiments, the trench 322 may reduce the transfer oftensile stress across the hanging area 332. Similarly, the one or moreopenings 340 may reduce the transfer of stress (e.g. compressive) fromthe surface mount substrate 312 across the hanging area 332. Thus, inaccordance with embodiments the hanging area 332, trench 322, andopening 340 may isolate the MEMS die 302 from mechanical stress.

In utilizing the various aspects of the embodiments, it would becomeapparent to one skilled in the art that combinations or variations ofthe above embodiments are possible for forming a MEMS package andmodule. Although the embodiments have been described in languagespecific to structural features and/or methodological acts, it is to beunderstood that the appended claims are not necessarily limited to thespecific features or acts described. The specific features and actsdisclosed are instead to be understood as embodiments of the claimsuseful for illustration.

What is claimed is:
 1. A package comprising: a surface mount substrate;an integrated circuit (IC) die mounted on a front side of the surfacemount substrate; a micro-electrical-mechanical systems (MEMS) diemounted on the front side of the surface mount substrate laterallyadjacent to the IC die; a molding compound that encapsulates the IC dieand the MEMS die on the front side of the surface mount substrate; and alanding pad arrangement including all landing pads on a back side of thesurface mount substrate, wherein the landing pad arrangement surrounds aperiphery of the IC die on the front side of the surface mount substrateand does not surround a periphery of the MEMS die on the front side ofthe surface mount substrate.
 2. The package of claim 1, furthercomprising a trench in a top surface of the molding compound between theIC die and the MEMS die.
 3. The package of claim 2, wherein a width ofthe trench is greater than a width of the MEMS die in a same direction.4. The package of claim 3, wherein the trench is formed entirely acrossa width of the molding compound.
 5. The package of claim 2, wherein abottom surface of the trench is below a top surface of the MEMS die. 6.The package of claim 1, further comprising a plurality of conductivepumps, with each landing pad having a corresponding conductive bump. 7.The package of claim 1, wherein the molding compound that encapsulatesthe IC die and the MEMS die does not cover a top surface of the MEMSdie.
 8. The package of claim 1, further comprising a metal trace on aback side of the surface mount substrate directly beneath the MEMS die,and a solder mask directly on the metal trace directly beneath the MEMSdie.
 9. The package of claim 1, wherein the molding compound is formeddirectly on the surface mount substrate.
 10. The package of claim 1,further comprising an opening in the surface mount substrate between theIC die and the MEMS die.
 11. The package of claim 10, wherein theopening has a width that is greater than a width of the MEMS die in asame direction.
 12. The package of claim 1, further comprising aplurality of openings in the surface mount substrate between the IC dieand the MEMS die.
 13. The package of claim 1, further comprising abumper on the back side of the surface mount substrate, the bumperformed of an elastomeric material.
 14. The package of claim 1, whereinthe MEMS die is attached to the surface mount substrate with a dieattach film.
 15. The package of claim 14, wherein the MEMS die is wirebonded to the surface mount substrate.
 16. The package of claim 1,further comprising: a trench in a top surface of the molding compoundbetween the IC die and the MEMS die; and an opening in the surface mountsubstrate between the IC die and the MEMS die.
 17. The package of claim1, further comprising a trench in a top surface of the molding compoundbetween the IC die and the MEMS die, wherein the MEMS die is attached tothe surface mount substrate with a die attach film.
 18. The package ofclaim 17, wherein the trench is slot shaped.
 19. The package of claim17, further comprising a bumper on the back side of the surface mountsubstrate, the bumper formed of an elastomeric material.
 20. The packageof claim 19, further comprising an opening in the surface mountsubstrate between the IC die and the MEMS die.